Short answers, pulled from the story.
The concept of monarchy emerged in ancient Mesopotamia over four thousand years ago. This development is documented on the Weld-Blundell Prism, a clay artifact inscribed with the Sumerian King List. The document lists kings who reigned for thousands of years before the Great Flood.
The Pope of the Roman Catholic Church serves as the sovereign of Vatican City State and represents the oldest surviving elective monarchy. This leader is elected for life by the College of Cardinals. The system allows a single ruler to exist without hereditary succession.
Sweden became the first monarchy to declare equal primogeniture in 1980. This change allowed the eldest child, regardless of gender, to ascend to the throne. Other kingdoms including the Netherlands, Norway, Belgium, Denmark, and Luxembourg followed suit in the decades that followed.
The English monarchy was temporarily overthrown by the Parliament of England in 1649. This event demonstrated the fragility of royal authority when faced with organized political opposition. The overthrow occurred before the American Revolution of 1776 and the French Revolution of 1789.
King Salman of Saudi Arabia broke centuries of tradition on the 21st of June 2017. He elected his son to inherit the throne instead of following the system of agnatic seniority. This system previously passed succession to the monarch's next eldest brother before moving to the monarch's children.
The Kingdom of Bhutan transitioned to a constitutional monarchy in 2008. This change marked a shift from absolute rule to a system with limited monarchical power. Japan, the world's oldest existing monarchy, has limited the power of the Emperor to a ceremonial role following its defeat in the Second World War.